Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 2555c Report Date: 09-May-96:17:11 Version: ********** Check-in Date: ********** 1.Proposal Title: CATACLYSMIC VARIABLES AND MILLISECOND PULSARS IN GLOBULAR CLUSTER CUSPS ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID STELLAR POPULATIONS GO Sub Category GLOBULAR CLUSTERS ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Prof. Jonathan E. Grindlay CFA USA 617-495-7204 PROFESSOR ------------------------------------------------------------------------------------ 7. Abstract We propose to use the PC to obtain H-alpha and comparison wide band red images of the nearby globular cluster NGC6752 which appears to be in an advanced stage of dynamical evolution. We will use these data for a color map analysis (Bailyn et al. 1988) and DAOPHOT crowded field photometry, in order to:(1) search for H-alpha emission objects including cataclysmic variables and nebulae surrounding millisecond pulsars (MSPs) and planetary nebulae, (2) search for diffuse H-alpha emission from a centrally concentrated population of the former two types of objects, and (3) study the radial distribution of H-alpha absorption line objects including faint blue horizontal branch stars (FBHBs). The central goal of our study is to test predictions of models for cluster dynamical evolution that predict the production of a substantial population of compact binaries due to a high rate of close stellar encounters in dense collapsed cluster cores. Our choice of one of this cluster that shows evidence of having undergone core collapse enhances the likelihood that the emission line objects expected from stellar encounters can be directly detected and resolved. Our search is distinctly different from, and more sensitive than, compact binary searches being planned by several GTO investigators. ------------------------------------------------------------------------------------ 8. Scientific Key Words: GLOBULAR CLUSTER, CORE COLLAPSE, STELLAR EVOLUTION, CATACLYSMIC VARIABLE, X-RAY BINARY, WHITE DWARF, NEUTRON STAR, MILLISECOND PULSA ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 2.60 par: 0 10. Num targs pri: 1 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: WF/PC ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 2555c PI: Prof. Jonathan E. Grindlay Proposal Title: CATACLYSMIC VARIABLES AND MILLISECOND PULSARS IN GLOBULAR CLUSTER CUSPS ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Haldan Cohn INDIANA UNIVERSITY USA Phyllis Lugger INDIANA UNIVERSITY USA P.I. Jonathan E. Grindlay CFA USA Charles Bailyn CFA USA ------------------------------------------------------------------------------------ 3. Description of proposed observations. We propose to obtain H-alpha (F656N) and comparison red (F675W) Planetary Camera (PC) frames of the central 1'x1' regions of the nearby globular cluster NGC6752 (4.1kpc). We plan a single placement of the PC field on the maximum symmetry center of the cluster, which we have determined from our ground based CTIO 4 meter PF-CCD data. Since a single exposure does not provide sufficient dynamic range, we plan two exposures in each filter: a short exposure to bring horizontal branch stars just up to the saturation level and a long exposure to reach a faint limiting magnitude. Our planned exposure times are detailed in section 5. ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. The high angular resolution provided by HST is essential for this project. Our goal is to detect individual emission line objects in the center of NGC6752, which shows evidence of having undergone core collapse. The core collapse simulations of Murphy and Cohn (1988) predict central stellar surface densities > 10**5 pc**-2. Adopting PSF FWHM vlues of 1.2" for ground-based observations and 0.09" for the HST PC at 6500A, the predicted number of stars per resolution element at the cluster center is of order 10-100 for ground based observations, but only of order 0.1 to 1 for the HST PC. Thus HST is critical for detecting individual emission line objects into the cluster center. We have obtained UBVR and H-alpha frames of this cluster using the PF-CCD on the CTIO 4 meter in seeing of 1.2"-1.4" (FWHM). We are currently constructing U/B and H-alpha/R maps which will be used to extend the HST coverage to more distant regions of the cluster. However, the spatial resolution of our ground-based data is clearly insufficient to explore the central 10"x10" region of NGC6752 which is where a population of CVs is expected to be concentrated. ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. We require a dynamic range of 10 magnitudes to cover stars from the horizontal branch to a limiting magnitude Mv=10 expected for millisecond pulsars. Since the Planetary Camera only provides a dynamic range of 7 magnitudes, we plan two exposures in each filter. The planned exposure times are summarized in the table below, which gives the corresponding limiting absolute magnitude for a 5 sigma detection above the read-out noise background. We adopt a read-out noise of 20e- per pix. The short exposures will bring horizontal branch stars (Mv=0.6) just up to the point of saturation. This will saturate the approximately 20 giants in the field. Assuming that only 2-4 CCD columns are lost per saturated star, this does not represent a large fraction of the 1500 column PC field. The long exposure in the red filter will reach Mv=12, while that in H-alpha will reach Mv=9 for a flat spectrum source. For an H-alpha emission object, the corresponding limiting Mv of an object detected in the H-alpha filter will be about 1 magnitude fainter. filter exposure time limiting absolute magnitude F656N 2700.0 6.5 F675W 40.0 7.0 F675W 1100.0 10.6 Page 3 ------------------------------------------------------------------------------------ 7. Data reduction and analysis plans. We have employed the technique of color mapping in our ground based observations with considerable success. After matching the PSF (by filter convolution) and registration, two frames are divided pixel by pixel, resulting in a map of the cluster by color rather than intensity. Very faint objects of unusual colors are then easy to detect, and indeed we have identified only the second optical counterpart to a cluster LMXB in this way (Bailyn et al. 1988). Since these maps measure the area emitting in a given color, rather than the magnitude of the star emitting it, color gradients can be examined without the large random fluctuations due to giants that plague aperture photometry. We have used color maps to demonstrate that the core of M15 is significantly bluer than its surroundings (Bailyn et al. 1989). We look forward to employing this powerful technique on the much higher resolution data obtainable with HST. In addition to color map analysis, we also plan to employ DAOPHOT PSF fitting to obtain photometry for all objects in each PC frame. Since the expected number of objects per resolution element is typically of order one or less, this procedure is appropriate for points sources of H-alpha emission. The Indiana University VAX 8842 (see section 10) will provide the necessary CPU capacity for this computationally intensive analysis. ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). The Harvard-Smithsonian Center for Astrophysics (CfA) has an extensive variety of computational facilities which will be used for analysis of the data obtained for this project. In particular, a fully supported network of SUN computers can be used although a dedicated node (SUN 3/60) is needed for the extensive analysis required. The SUN network supports a full implementation of IRAF, DAOPHOT, and additional processing and spectroscopy analysis software. The SUN network is connected (via Ethernet) to a microVAX net as well as a convex machine. There is also a high speed link between the CfA and the Supercomputer network. The Indiana University Astronomy Department has developed a powerful microVAX based image processing system, largely with University funding. This system runs IRAF and SDAS software, including DAOPHOT. In addition, Indiana University has recently acquired a VAX 8842 (equivalent to 24 VAX 780's) which will provide substantial additional CPU capacity for manipulating ST images, at no cost to this proposal. Indiana University funds a high speed link (1.5Mbps) to the National Center for Supercomputing Applications (NCSA), where we are carrying out simulations of globular cluster dynamical evolution in support of this proposed HST program. ------------------------------------------------------------------------------------ 11. Address Information Name: JONATHAN E. GRINDLAY Category: PI Institution: HARVARD UNIVERSITY Address: 60 GARDEN STREET City: CAMBRIDGE State: MA Zip Code: 02138 Country: USA Telephone: Telex (or e-mail): ------------------------------------------------------------------------------------ TARGET LIST a) Fixed Targets ID = 2555c [ 4] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial |Acqui|FLX| Flux data No | Name | Description | Position |Eqnx | Vel. |Prblm|REF| | | | | | | | | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6752 STAR CLUSTER RA = 19H 06M 27.3S +/- 1S, 1950 1 V= 12 +/- 0.5 GLOBULAR CLUSTER DEC = -60D 03' 50.5" +/- 1" ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 2555c [ 5] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6752 PC IMAGE ALL F656N PRE-FLASH=YES 3 2700S 1 1 CYCLE 1 /1-3 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6752 PC IMAGE ALL F675W PRE-FLASH=YES 1 40S 1 1 ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC6752 PC IMAGE ALL F675W 1 1100S 1 1 ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 2555c [ 6] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations PC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters PRE-FLASH ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 2.60 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category STELLAR POPULATIONS ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category GLOBULAR CLUSTERS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CYCLE 1 /1-3 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F656N F675W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC6752 ------------------------------------------------------------------------------------------------------------------------------------